I am a guitar enthusiast and a hobbyist player. The majority of my projects happen around guitar paraphernalia. I build my owns amps and some effect pedals.

In the past I played in a small band and convinced myself that I only needed an amp with a reverb, a clean channel and a dirty channel, and a tube screamer pedal to boost my guitar for soloing. I avoided having several pedals because I am sloppy and wouldn't engage the correct ones, I do not know how to tap dance.

The other problem that happens with having several pedals in a chain is that some of them are not true by-pass. As a result, if you don't use a buffer you will lose some definition in the signal, even when the pedals are not engaged. Some common examples of these pedals are: my Ibanez TS-10, a Crybaby Wah, a Boss BF-3 Flanger, you get the idea.

There are digital pedalboards that allow you to setup individual buttons for a pre-defined combination of digitally simulated effects. But, dealing with programming a digital platform, loading patches, setups, etc. bother me big-time. Besides, they are definitely not true bypass.

Finally, I already have pedals and I like them individually. I can setup the pedal I want and change its presets without the need of a computer (or my phone).

All of this prompted a search several years ago, I started looking for something that would:

Look like a pedalboard with each individual button assigned to a combination of my analog pedals.

Convert all my pedals to true bypass when they are not used.

Use some setup technology that would not require the use of midi patches, computers, or anything attached.

Be affordable.

I found a product by Carl-Martin called Octa-Switch that was exactly what I wanted, at almost $430 it was and still is not for me. Anyways, it is going to be the base of my design.

I think that it is possible to build a platform with my requirements, for less than a quarter than buying it from the store. I do not have an Octa-Switch, never owned one, or play with it, so I do not know what is inside. This is my own take.

For the schematics, layout and PCB design I will be using both DIYLC, and Eagle. I will use DIYLC for wiring designs that not need PCB, Eagle for the final design and PCB.

I hope you enjoy my journey.

Step 1: How to Make the Guitar Signal Bypass a Pedal on a Chain of Pedals (True Bypass)

This simple circuit allows you to bypass a pedal using a 9-pin 3PDT Foot Switch and 4 input jacks (1/4 mono). If you want to add an on/off LED, you will need: an LED, a 390 Ohms 1/4 watt resistor, a battery holder for 9V, and a 9 volts battery.

Using the cheapest components found in Ebay (at the moment of writing this Instructable), the total price is:

The way this circuit works is very intuitive. The signal from the guitar enters X2 (input jack). In rest position (effect pedal not engaged), the signal from X2 bypasses the pedal and goes directly to X4 (output jack). When you activate the pedal, the signal enters X2, goes to X1 (out to pedal input), returns through X3 (in from pedal output)and exits via X4.

IMPORTANT: For this box to work properly the effect pedal should be always ON

The LED turns on when the signal goes to the effect pedal.

Step 2: Using Relays Instead of the On/Off Switch

Using Relays

Expanding on the simple on/off switch idea, I wanted to be able to bypass simultaneously more than 1 pedal. One solution would be to use a foot switch that have several DPDT in parallel, one switch per pedal to be added. This idea is impractical for more than 2 pedals, so I discarded it.

Another idea would be to trigger several DPDT switches (one per pedal) at the same time. This idea is challenging because it means that one should simultaneously activate as many footswitches as pedals needed. As I said before, I am not good at tap dancing.

The third idea is an improvement on this last one. I decided that I could trigger low signal DPDT relays (each relay acts as a DPDT switch), and combine the relays with DIP switches. I could use a DIP switch with as many individual switches as relays (pedals) are needed.

In this way I will be able to select what relays I want to activate at any given time. In one end, every individual switch in the DIP switch will connect to the coil of the Relays. On the other end, the DIP Switch will connect to a single on off switch.

Fig 1 is the complete schematic for 8 Relays (8 pedals), Fig 2 is the detail of the switch section of Relay 1 (K9), and the 3rd file is the Eagle Schematic.

It is easy to see that the bypass section (Fig 2) is exactly the same circuit as the one discussed in Step 1. I kept the same denomination for the jacks (X1, X2, X3, X4), so the explanation of how the bypass work is the same word by word than the one for Step 1.

Activation of the relays:

In the complete schematics for 8 relays (Fig 1) I added switch transistors (Q1 - Q7, Q9), polarization resistors to set the transistors as On-Off switches (R1 to R16), an 8 switches DIP Switch (S1-1 to S1-8), an on/off switch (S2) and the LEDs that indicate what relays are on.

With S1-1 to S1-8 the user selects what relays will be activated.

When S2 is active, the transistors selected by S1-1 to S1-8 are saturated via the polarization Resistors (R1-8).

In saturation VCE (DC voltage between collector and emitter) is approximately "0 V", so VCC is applied to the selected relays turning them on.

This part of the project could be done without the transistors, using the DIP Switch and the S2 to either VCC or Ground. But I decided to use the complete circuit so there is no need for further explanation when the logic part is added.

The diodes in reverse, parallel to the relays' coils, protect the circuit from the transients generated with the activation/deactivation of the relays. They are known as fly back or flywheels diodes.

Attachments

Step 3: Adding More Pedal Combinations (AKA More DIP Switches)

The next step was to think how to add more versatility to the idea. In the end I want to be able to have several possible combinations of pedals that are selected by pressing different foot switches. For example I want to have pedals 1, 2 and 7 working when I press one foot switch; and I want pedals 2, 4 and 8 when I press another.

The solution is to add another DIP Switch and another foot switch, Fig 3. Functionally it is the same circuit than the one explained in the previous STEP.

Analyzing the circuit without diodes (Fig 3) one problem appears.

S2 and S4 select what DIP switch will be active and each DIP switch which combination of relays will be on.

For the 2 alternatives described in the first paragraph of this STEP the DIP Switches should be set as follows:

S1-1: ON; S1-2: ON; S1-3 to S1-6: OFF; S1-7: ON; S1-8: OFF

S3-1: OFF; S3-2: ON; S3-3: OFF; S3-4: ON; S3-5 TO S3-7: OFF; S3-8: ON

When pressing S2, those S1-X switches that are ON will activate the correct relays, BUT S3-4 and S3-8 will also be activated via the shortcut S1-2 // S3-2. Even though S4 is not grounding S3-4 and S3-8, they are grounded via S3-2.

The solution to this problem is to add diodes (D9-D24) that will be opposing any short cut (Fig 4). Now in the same example when S2-2 is at 0 V D18 is not conducting. It does not matter how S-3 and S3-8 are setup, D18 will not allow any flow of current. Q3 and Q7 will remain off.

Fig 5 is the complete relay section of the design including 2 DIP Switches, 2 Foot Switches, and the diodes.

The Eagle Schematic for this section is also included.

Attachments

Step 4: Adding Logic and Momentary Switches (Pedalboard)

Although the simple circuit explained so far can be extended with as many DIP switches as combination of pedals are wanted, there is still a drawback. The user needs to activate and deactivate the footswitches one by one according to the combination required.

In other words, if you have several DIP Switches, and you need the pedals on DIP Switch 1, you have to activate the associated foot switch and disengage any other footswitch. If not, you will be combining the effects in as many DIP switches as you have active simultaneously.

This solution makes the user's life easier in the sense that with only 1 footswitch you can activate several pedals at the same time. It does not require you to activate each effect pedal individually. The design can still improve.

I want to activate the DIP switches not with a foot-switch that is always on or off, but with a momentary switch that "remembers" my selection until I select another DIP Switch. An electronic "latch".

I decided that 8 different configurable combinations of 8 pedals will suffice for my application and it makes this project comparable to the Octa-switch. 8 different configurable combinations mean 8 footswitches, 8 pedals mean 8 relays and associated circuitry.

Choosing the latch:

I chose the Octal edge triggered D type Flip Flop 74AC534, this is a personal choice and I assume that there might be other IC's that will also fit the bill.

According to the datasheet: "On the positive transition of the clock (CLK) input, the Q outputs are set to the complements of the logic levels set up at the data (D) inputs".

Which essentially translates to: every time the pin CLK "sees" a pulse going from 0 to 1 the IC "reads" the state of the 8 data inputs (1D to 8D) and sets the 8 data outputs (1Q/ to 8Q/) as the complement of the corresponding input.

In any other moment, with OE/ connected to ground, the data output maintains the value read during the last CLK 0 to 1 transition.

Input Circuit:

For the input switch I chose SPST Momentary Switches ($1.63 in eBay), and set them up as shown in Fig 6. It is a simple Pull down circuit, with a de-bounce capacitor.

At rest, the Resistor pulls the output 1D to VCC (High), when the momentary switch is activated 1D is pulled down to ground (Low). The capacitor eliminates transients associated with the activation/deactivation of the momentary switch.

Putting the pieces together:

The last piece of this section would be to add Schmitt-Trigger inverters, which will: a) provide a positive pulse to the Flip Flop input, b) further clear any transient produced during the pedal switch activation. The complete diagram is shown in Fig 7.

Finally I added a set of 8 LED's in the Flip Flop outputs that go "ON" showing what DIP Switch is selected.

The Eagle schematic is included.

Attachments

Clock Signal Generation

For the clock signal I decided to use "OR" gates 74LS32. When any of the inverters' outputs is 1 (switch pressed) the pin CLK of the 74LS534 see the change from low to high generated by the chain of OR gates. This chain of gates also produces a small delay of the signal reaching CLK. This assures that when the CLK pin of the 74LS534 sees the signal going from low to high, there is already a High or Low state in the inputs.

The 74LS534 "reads" what inverter (momentary switch) is pressed, and puts a "0" in the corresponding output. After the transition from L to H in the CLK the state of the 74LS534 output is latched until the next cycle.

Complete design

The complete design also includes LED's that indicate what pedal is active.

Fig 8 and schematics included.

Attachments

Step 6: Board Designs (using Eagle) - Control Logic Board

I will design 3 different boards: 1) the control logic, 2) the DIP switches board, 3) the relays and output board.

The boards will be connected using simple point to point wires (18AWG or 20AWG) should work. The points of connection between the boards themselves and the boards with external components I am using: 8 pins Molex connectors for the data busses, and 2 pins for the 5V power supply. This helps with the Eagle design.

The control logic board will include the resistors and capacitors needed for the de-bounce circuit.

The DIP switches board will include the DIP switches and the LEDs connections.

The relays and output board will include the polarization resistors, the transistors and the relays.

The momentary switches and the 1/4 jacks are external and will be connected to the board using point to point wire connections.

Control logic board

There is no special concern for this board, I only added standard resistors and capacitors values for the de-bounce circuit.

BOM

Partlist

Assembly

variant:

Part

Value

Device

Package

QTY

C1

10n

C-EU050-025X075

C050-025X075

1

C2

10n

C-EU050-025X075

C050-025X075

1

C3

10n

C-EU050-025X075

C050-025X075

1

C4

10n

C-EU050-025X075

C050-025X075

1

C5

10n

C-EU050-025X075

C050-025X075

1

C6

10n

C-EU050-025X075

C050-025X075

1

C7

10n

C-EU050-025X075

C050-025X075

1

C8

10n

C-EU050-025X075

C050-025X075

1

IC1

7414N

7414N

DIL14

1

IC2

7414N

7414N

DIL14

1

IC3

7432N

7432N

DIL14

1

IC4

7432N

7432N

DIL14

1

IC5

74AC534N

74AC534N

DIL20

1

R17

10K

R-US_0207/10

resistor

1

R18

10K

R-US_0207/10

resistor

1

R19

10K

R-US_0207/10

resistor

1

R20

10K

R-US_0207/10

resistor

1

R21

10K

R-US_0207/10

resistor

1

R22

10K

R-US_0207/10

resistor

1

R23

10K

R-US_0207/10

resistor

1

R24

10K

R-US_0207/10

resistor

1

X1

22-23-2081

22-23-2081

22-23-2081

con-molex

1

X2

22-23-2081

22-23-2081

22-23-2081

con-molex

1

X3

22-23-2021

22-23-2021

22-23-2021

con-molex

1

Attachments

Step 7: DIP Switch Board

Because the board area id limited when working with the free distribution of Eagle, I decided to divide the dip switches into 2 groups of 4. The board that accompanies this step contains 4 DIP switches, 4 LEDs that indicate which DIP switch is active (what foot-switch was pressed last), and a power led to indicate that the pedal is "ON'.

Attachments

Step 8: Relay Board

Estimating the polarization resistors value

At this point I need to calculate the value of the polarization resistors that connect to the transistors. For a transistor to be saturated.

The relays that I am using are the JRC 27F/005S. The coil consumes 200mW, the electrical characteristics are:

Order Number

Coil Voltage VDC

Pick-up Voltage VDC (Max.)

Drop-out Voltage VDC (Min.)

Coil Resistance ±10%

Allow Voltage VDC (Max.)

005-S

5

3.75

0.5

125

10

IC = 200mW / 3.75 V = 54 mA

IB = 54mA/HFE = 54mA / 125 (minimum HFE for the BC557) = 0.44 mA

Using the circuit in Fig 9:

R2 = (VCC - VBE - VD1) / (IB * 1.30) -> Where VCC = 5V, VBE is the voltage of the Base-Emitter junction, VD1 is the Voltage of the Diode D1 on direct. This diode is the diode that I added to avoid activating relays incorrectly, explained in Step 3. To assure saturation I will use the maximum VBE for the BC557 which is 0.75 V and increase the IB current by 30%.

Attachments

Step 10: Additional Resources - DIYLC Design

I decided to make a 1st prototype of the design using DIYLC ( http://diy-fever.com/software/diylc/ ). It is not as powerful as Eagle, the big disadvantage being that you cannot create the schematic and generate the board layout from it. In this application you have to design the PCB layout by hand. Also if you want somebody else to make the boards, most companies only accept Eagle designs. The advantage is that I can put all the DIP switches in 1 board.

I used double layered Copper Clad PCB for the logic board and single layered copper clad PCB for the DIP Switch Board and Relay Board.

In the board design I am adding an example (circled) of how to connect the LEDs that will indicate which of the DIP Switches is ON.

To make the PCBs from DIYLC you have to:

1) Select the board to work on (I am providing the 3 boards as before) and open it with DIYLC

2) In the Tool Menu, select "File"

3) Under the "File" tab select "Trace Mask"

4) You can export the board layout to PDF or PNG. An example of the Logic Board layout exported to PDF is included.

5) To use the transfer method to your copper clad PCB, you need to print this without scaling. Also you need to change the color of the components side layer from green to black.

6) DO NOT forget to mirror the components side of the board to use the transfer method.